Improving repair performance for damaged C/C composites via heat-treatment temperature optimization and surface pretreatment

A Ni-based solder BNi-5 was adopted as the repair agent to repair the prefabricated defects on the carbon/carbon (C/C) composites. The effects of different heat-treatment (HT) temperatures and pre-oxidation on the chemical composition, microstructure, and mechanical behavior of the repaired C/C composites were investigated, and the repair mechanism was studied by finite element analysis methods. The repair agent and C/C composites were tightly bonded through mechanical interlocking and chemical reactions, and the flexural properties of the damaged C/C composites were significantly improved after repair. The products at the interface formed a gradient distribution structure of the thermal expansion coefficient when the HT temperature was 1300 degrees C, which is beneficial to relieve the residual thermal stress at the interface. Meanwhile, the porosity of the surface of the C/C composites was higher after pre-oxidation, which led to more diffusion channels for the repair agent and enhanced the interface bonding ability. The flexural strength was the highest with a recovery rate of 85.2% when the C/C composites were preoxidized at 600 degrees C and the HT temperature was 1300 degrees C. This work provides a strategy for the engineering application of the damage repair of C/C composites. (c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.